Synergistic Effects of Polystyrene Nanoplastics and Cadmium on the Metabolic Processes and Their Accumulation in Hydroponically Grown Lettuce (Lactuca sativa)

Plastic contamination in agricultural systems is an emerging concern. While current research suggests low direct toxicity, the consequences from interactions between nanoplastics and copresent contaminants are poorly understood. In this study, the synergistic effects of cadmium (Cd) and polystyrene nanoplastics (PS NP) on the growth and physiological responses of hydroponically grown Lactuca sativa (lettuce) were examined. Coexposure significantly increased the accumulation of Cd and PS NP by 61 and 67% in lettuce shoots compared with single-contaminant exposure. Metabolomic analysis showed that joint exposure induced an increase in glutathione and flavonoid-like compounds, suggesting an energy-intensive oxidative stress response. In addition, coexposure appeared to promote adventitious root formation, as evidenced by an increased abundance of metabolites linked to nitric oxide signaling. These findings suggest that the projected increase in PS NP in agricultural environments could exacerbate Cd uptake in food crops, potentially increasing human dietary exposure to heavy metals.